The rapid global spread of modern cellular communication systems has been primarily driven by three factors: standardisation, cost and performance. The availability of universal communication standards promulgated by organisations such as 3rd Generation Partnership Project (3GPP) allows manufacturers to produce a single product for a global market. The low cost of cellular communications is primarily due to the high levels of functional integration achievable in modern microchip technology and the size of the global market which offers significant economy of scale benefits to manufacturers. The high performance of cellular communications is achieved through exploitation of the functional capabilities of modern semiconductor technology.
Increased functional integration in a radio transceiver leads to the analog and digital functions of the radio transceiver being closely located to each other. It is well known in the prior art that reduced physical separation between radio circuit components leads to an increase in mutual self-interference. Typically, a digital clock will consist of a train of rectangular pulses and will be rich in harmonic content. The integration of digital circuit elements which utilise a digital clock can therefore lead to radio frequency (RF) interference at harmonic frequencies of the digital clock. Typically, the transceiver will be most vulnerable to this type of interference when it tries to receive low power signals at RF frequencies at or close to harmonics of any digital clock used in the transceiver.
Modern cellular radio transceivers are required to operate in a plurality of frequency bands. It is also necessary for a modern transceiver to achieve the desired performance levels required by standards such as 3GPP, and it is therefore necessary for the modern transceiver to contain a significant digital signal processing capability. Furthermore, as it is expensive and time consuming to develop a radio transceiver in an advanced semiconductor manufacturing process, it is a desirable requirement that a radio transceiver be sufficiently flexible to operate in frequency bands that might in the future be designated as cellular bands by the standardisation authorities.
U.S. Pat. No. 5,926,514 discloses changing a clock signal used by a microcontroller unit in a radio transceiver in response to changes in the operating frequency of the radio transceiver.
U.S. Pat. No. 7,103,342 discloses changing a clock signal used by a microcontroller unit in a radio transceiver in order to minimise interference at the selected operating frequency of the radio transceiver.
U.S. Pat. No. 6,898,420 discloses toggling a clock signal used by a microcontroller between two possible frequencies.
U.S. Pat. No. 7,676,192 discloses a technique to change the operating frequency of a device and the signal frequency of a co-located signal source in order to minimise interference that is introduced on the wireless interface of that device.
There remains a need for techniques which can be employed to address the impact of clock harmonic interference in a radio transceiver.